1. Field of the Invention
The present invention relates to image forming apparatuses such as copiers, printers, and facsimiles, and in particular, relates to apparatuses including detecting devices for detecting recording materials.
2. Description of the Related Art
An apparatus for controlling an image forming section on the basis of detection results produced by a sheet detecting unit disposed before the image forming section, for example, before a transferring position at which images are transferred onto a sheet, is disclosed in, for example, Japanese Patent Laid-Open No. 10-329984.
Such a sheet detecting unit generally includes a sensor disposed on a sheet-feeding route for detecting sheets, and detects a sheet while the sheet is carried after being separated from the other stacked sheets.
Some types of sheet require time before being detected by the sensor and the optimum image forming conditions are set. When the distance to the image forming section becomes longer for the detection and the setting, the entire apparatus becomes disadvantageously larger. The sheets may be temporarily stopped at a predetermined position on the feeding route for the time required for sheet detection, but it takes too much time to form images on only one sheet.
To avoid this, an apparatus disclosed in Japanese Patent Laid-Open No. 2004-2017 detects sheets at a position of a sheet cassette that is located at the most upstream portion of the sheet-feeding route. In this apparatus, the sensor moves linearly, and thus can correctly detect the sheets regardless of the volume of stacked sheets.
However, the sensor in the apparatus disclosed in Japanese Patent Laid-Open No. 2004-2017 does not face a pressure plate that pushes the sheets against a feeding roller. Therefore, small-sized sheets that are mainly stacked at the position of the pressure plate may not be detected. The pressure plate changes the inclination of the sheets according to the volume of the stacked sheets. However, the sensor according to Japanese Patent Laid-Open No. 2004-2017 cannot respond to the inclination change.